The present invention relates to a polarization rotation compensator and to an optical isolator using the polarization rotation compensator. More particularly, it relates to a polarization rotation compensator which is capable of rotating a plane of polarization by a desired angle when linearly polarized light is passed therethrough, and which is and capable also of compensating for deviations in the polarizing angle due to deviations of the optical wavelength in the incident ray and due to the effect of an optical isolator which is not dependent on the wavelength change in the incident ray.
As is well known, a rotator used in an optical device such as an isolator for optical communication at a wavelength of 1.30 .mu.m (microns), for example, has a wavelength dependency. In an optical isolator, for example, when linearly polarized light passes through a 45-degree Faraday rotator, a plane of polarization rotated 45 degrees about the direction of propagation thereof can be obtained. However, this is possible only for light having a predetermined wavelength. Deviation in the wavelength of the light causes the polarizing angle of the plane of polarization to deviate, resulting in deterioration of the isolation effect of the isolator.
Crystal quartz, polarization rotation compensator which correct deviations in the optical rotating angle of a plane of polarization due to wavelength deviations are well known in the art.
However, although a crystal quartz, polarization rotation compensator whose principal axis is parallel to the propagating light can correct deviations in the optical rotating angle, they are large, having a length, for example, of 10 mm to 15 mm along the optical axis when they are used for the long wavelength above.